Low RPM motor solution... finally!

[absolom7691]

Not sure if this forum is dead now or not, but I figured I would post here anyway. I ditched the A4988 drivers for the TMC2209 drivers. Night and day difference. Set to stealthchop and 1/64 steps, I don't even need a reduction gearbox anymore. Direct drive eliminates any gearbox stiction or hiccups due to cheap grease/cheap quality. I can get a 1.8° stepper down to around .07 RPM, pulsing the driver at 10hz, and the results are still liquidy smooth. With a 0.9° stepper, I was able to go even slower. Interference patterns moved like wisps of smoke in a room with no wind. For flowing water, 500hz will get you about 2 RPM, still smooth. For anyone who still visits here, this is a complete win for building a lumia projector.

[swamidog]

Not sure if this forum is dead now or not, but I figured I would post here anyway. I ditched the A4988 drivers for the TMC2209 drivers. Night and day difference. Set to stealthchop and 1/32th steps, I don't even need a reduction gearbox anymore. Direct drive eliminates any gearbox stiction or hiccups due to cheap grease/cheap quality. I can get a 1.8° stepper down to around .07 RPM, pulsing the driver at 10hz, and the results are still liquidy smooth. With a 0.9° stepper, I was able to go even slower. Interference patterns moved like wisps of smoke in a room with no wind. For flowing water, 500hz will get you about 2 RPM, still smooth. For anyone who still visits here, this is a complete win for building a lumia projector.

sweet! got a link?

[absolom7691]

sweet! got a link?

Sure do! They can be found on Amazon:
https://www.amazon.com/Teyleten-Robo...l%2C189&sr=1-5

Documentation link:
https://learn.watterott.com/silentst...onfig/tmc2209/

Here's a video showing the operation using a nema 11 stepper:

[swamidog]

that is awesome... time to up my lumia game.

Sure do! They can be found on Amazon:
https://www.amazon.com/Teyleten-Robo...l%2C189&sr=1-5

Documentation link:
https://learn.watterott.com/silentst...onfig/tmc2209/

Here's a video showing the operation using a nema 11 stepper:

[absolom7691]

I do need to make a correction... I was running at 1/64 microstepping, Not 1/32. My apologies. I'm trying to see how slow I can get this to move. So far, pulsing at 2hz, I'm at .014 RPM. That's about ~0.84 RPH! Sadly, it's not smooth, which I expected. For a 1.8° stepper, I think .05 RPM is the limit while still being smooth. Still, that's only 3 RPH!

[buffo]

I'm really impressed with those results, Bryan! Although I can't help but think that things would be even better with one of the planetary gearbox steppers attached to that driver. Interesting that you mentioned an issue with the gears sticking - I haven't experienced that myself, but I've only run mine for bench tests thus far... Hope this isn't a common problem with the planetary gearboxes. (Maybe I should pull the cover and re-grease them?)

The last time we messed with this at SELEM, I was using this driver: https://www.amazon.com/Stepper-Drive.../dp/B0FFGGJTYX and this frequency generator to run it: https://www.amazon.com/dp/B07P848DYQ

The drivers run about $10 bucks each, and they're roughly the size of a deck of cards. The frequency generator units are designed to be mounted on a panel and look really sharp, and at ~$15 they're on par with just about any other PWM source you can find.

What we found was that below about 200 Hz on the input you couldn't really see the movement of the lumia pattern on the wall unless you watched it very closely, but if you ramped it up to around 9000 Hz you could get something that looked like flames. Thanks to Zac (Laserman121) Collins, we had both a red and a yellow laser feeding into the lumia wheel, and that looked amazing. The sweet spot seemed to be around 1500 Hz or so for typical lumia. But there was never any stutter or jerking in the pattern, even when it was running far slower than you'd ever want for lumia.

It seems that at the slowest settings on your rig, there is a barely perceptible jerk as the stepper notches forward tooth by tooth, but admittedly, I'm nit-picking. I'm never going to run lumia anywhere near that slow, so it wouldn't ever be an issue. But as I've already bought 5 of those planetary gearbox stepper motors, I think I'm going to stick with those, lol! (Now I just need to actually build something.)

Adam

[absolom7691]

I'm really impressed with those results, Bryan! Although I can't help but think that things would be even better with one of the planetary gearbox steppers attached to that driver. Interesting that you mentioned an issue with the gears sticking - I haven't experienced that myself, but I've only run mine for bench tests thus far... Hope this isn't a common problem with the planetary gearboxes. (Maybe I should pull the cover and re-grease them?)

For me, I was just looking for more room in my projector and heard good things about these drivers. Direct-drive just seemed like a better idea. I don't even have to think about the gearbox now. I don't need to worry about any backlash or any artifacts. Reversing directions, I don't need to wait for the slop in the gearbox to catch up.

**Warning** don't bother opening the gearbox. They're a bitch to get open! Both ends are press-fitted with some epoxy to seal them. Speaking from experience!!!

What we found was that below about 200 Hz on the input you couldn't really see the movement of the lumia pattern on the wall unless you watched it very closely

This is why I ditched the gearbox. It just isn't needed. I'm never going to be driving a lumia that slowly. Besides, a nema 8 motor is $20~$25. Stick one of those planetary gearboxes on it and the price doubles. This is just a cheaper option.

It seems that at the slowest settings on your rig, there is a barely perceptible jerk as the stepper notches forward tooth by tooth, but admittedly, I'm nit-picking. I'm never going to run lumia anywhere near that slow, so it wouldn't ever be an issue. But as I've already bought 5 of those planetary gearbox stepper motors, I think I'm going to stick with those, lol! (Now I just need to actually build something.)

You're right, and it wasn't until a closely watched the video before I saw it. This nema 11 I used in the video is good to .8A. I had mine at about 150ma to run stone cold since there was next to no load. The 150ma current wasn't enough to prevent the magnetic cogging. I upped the current to about 400ma and the cogging disappeared. Likewise though, I won't be running my lumia at .05 RPM! lol It's just way too slow! I'll see if I can get better video on the wall. That should amplify any adverse artifacts. I'll post later when I get some time.

Yeah, if you already have the the gear reduction motors, don't change up unless they give you trouble.

[absolom7691]

This looks great! Thanks for sharing, Bryan.

Thanks! Just trying to share the info!

@Adam, I took an updated video with the projection on the wall. I scrutinized the pattern carefully and this time it was absolutely liquid smooth. If there is any stutter in the video, it's got to be compression artifacts. Regardless, this is what it looks like. I'm running an Itty bitty nema 8 motor at about 300ma. Pulsing at about 15hz, 0.07 RPM.

[buffo]

Hey Bryan,

Yeah, I bought 5 of those steppers with the planetary gearboxes attached back when you first discovered them. But they were only like $35 bucks a pop or so, which wasn't too bad. (Still, they've been mostly sitting in a box for the last 3 years - sigh.)

Regarding the stuttering I saw in the video, I'm starting to think this might be an artifact caused by the Youtube compression rather than actual cogging of the stepper motor. In the latest video you posted, I still noticed some stuttering, although when I loaded the video on Youtube itself and played it full-screen, it was almost completely gone. The fact that it got better with full-screen playback suggests that this is a Youtube issue. And really, it's almost imperceptible - no way I'd notice it if the video wasn't zoomed all the way in like that.

Man, I really need to fish out the box of Lumia parts and get something assembled. It's been far too long! (Especially after Greg spent so much time and effort locating the lumia glass and cutting all those wheels a few years ago...) Makes me wonder if the lasers are still good.

Adam

[absolom7691]

That's the curse we all have, "If I only had more time... " I still haven't finished my lumia projector! I broke ground, made great progress and have even sat back and watched it paint some great photons. Alas, it's still not complete!

I've been playing around with a 65mm diamond hole saw and was finally able cut a piece of patterned glass without breaking it. Man, that takes forever. Soda lime glass is the worst! I turn the hose to a trickle and let it wash over the glass and saw, run the drill at about 1 RPM and just let the weight of the drill do the work. Any pressure beyond that will result in breaks. Takes about 25 minutes per wheel, so I can see the trouble Greg went through!! By contrast, torture tubes are infinitely easier!! I use the little 4ml borosilicate vials and MAPP gas. Easy peasy!